In the conventional method of stopping a polymer electrolyte fuel cell (hereinafter referred to as PEFC), supply of an oxidizing agent and a reducing agent is stopped and these materials remaining within the PEFC stack are purged by, for example, an inert gas such as nitrogen (see patent document 1). Thereafter, during a stopped state of the PEFC, an oxidizing agent passage and a reducing agent passage are typically filled with the inert gas or the like to inhibit entry of air into the PEFC stack (see patent document 2). Thereby, oxidization of an electrode catalyst layer within the PEFC stack and degradation of performance of the PEFC are inhibited. In addition, there has been disclosed a method of preserving the PEFC while maintaining a potential of a separator at a predetermined value during a power generation stopped state of the PEFC (see patent document 3).
When a membrane-electrode-assembly (MEA) is created, an electrode catalyst layer is formed by applying a coating material for formation of a catalyst layer onto a surface of a polymer electrolyte fuel cell membrane. The coating material for formation of the catalyst layer contains an alcoholic component as a solvent. As catalyst powder, for example, carbon powder carrying platinum-ruthenium alloy particles or platinum particles is used. The catalyst powder is mixed with an ethyl alcohol dispersion containing perfluorocarbonsulfonic acid polymers and produced into a paste. The paste is applied to a surface of the polymer electrolyte membrane to form the electrode catalyst layer. The solvent containing the alcohol component enters a part of a porous electrode catalyst layer and remains there after manufacturing the MEA.
As a method of improving a drawback that an ion resistance at an interface between the polymer electrolyte membrane and the electrode catalyst layer increases, and a drawback that an electron resistance at an interface between the electrode catalyst layer and a diffusion electrode layer increases because the electrode catalyst layer and the diffusion electrode layer are not firmly joined to each other, there has been disclosed a method of heating, pressurizing and integrating an element including a polymer electrolyte membrane sandwiched between two electrodes in a solvent (see e.g., patent document 4). Furthermore, there has been disclosed a method of heating and pressurizing a polymer electrolyte membrane and/or an electrode catalyst layer containing a solvent substantially without being immersed in the solvent (see e.g., patent document 5). In accordance with this method, because the solvent within a MEA vaporizes during a step of integration, swelling of the polymer electrolyte membrane that is due to the solvent is controlled, maintaining a desired joint state at the interface between the polymer electrolyte membrane and the catalyst layer.    [Patent Document 1] Japanese Laid-Open Patent Application Publication No. Hei. 6-251788    [Patent Document 2] Japanese Laid-Open Patent Application Publication No. Hei. 7-272738    [Patent Document 3] Japanese Laid-Open Patent Application Publication No. 5-258762.    [Patent Document 4] Japanese Laid-Open Patent Application Publication No. Hei. 3-208262    [Patent Document 5] Japanese Laid-Open Patent Application Publication No. 2002-93424